1. Field of the Invention
This invention relates to a flow control apparatus for use in a gas supply mechanism or the like.
2. Description of the Related Art
Many conventional gas supply mechanisms for supplying a given gas at a predetermined flow rate have a flow control apparatus, i.e., a mass flow controller, equipped with a flow detecting sensor for sensing the flow of a gas, a gas flow adjusting mechanism, and a control mechanism for controlling the gas flow adjusting mechanism in accordance with a flow detection signal supplied from the flow detecting sensor.
In the field of semiconductor device manufacturing, for example, the above-described flow control apparatus is employed in a gas supply mechanism used in a treatment apparatus for performing coating of a semiconductor wafer or other treatments.
Such a flow control apparatus employs a gas flow adjusting mechanism for reducing the flow of gas by reducing the cross section of the gas flow passage, i.e., restricting its size. There is possibility that a gas becomes liquefied or reacts in the gas flow adjusting mechanism, in which case the adjusting mechanism may become clogged stopping the flow of gas.
In the event of such a problem occurring, it is necessary to close the valves located upstream and downstream of the flow control apparatus, then to detach the control apparatus from the pipe arrangement, and to eliminate the problem. However, in the case where the gas is flammable or noxious, it is necessary to prevent it from leaking to the outside by using nitrogen gas, for example, to purge the gas remaining in a portion of the pipe in the vicinity of the flow control apparatus before the control apparatus is detached from the pipe arrangement.
However, if the gas passage of the flow control apparatus is closed, purging gas will not be able to flow through it. In order to deal with such a problem, a bypass pipe 4, as shown in FIG. 1, is connected to a gas supply pipe 2 across which the flow control apparatus (mass flow controller) 1 is arranged, such that it bypasses the apparatus 1. The bypass pipe 4 has a closing valve 3 which is closed in a normal state, and opened to allow the purging gas to flow through it if the flow control apparatus is clogged up. Closing valves 5 are provided across the pipe 2 at locations upstream and downstream of the flow control apparatus 1.
It is desirable that the manufacturing cost of the above-described gas supply mechanism be kept as low as possible by decreasing the number of its components, and also to reduce the possibility of gas leakage by decreasing the number of connecting portions of the pipe arrangement. Further, in the case of a semiconductor manufacturing apparatus such as, in particular, a vertical-type thermal treatment apparatus, it is desirable that the apparatus be as compact as possible in order to minimize the space required for installation, and accordingly reduce the size of the gas supply mechanism.